Sebastian Aleksandra, Harley William, Fox Alvin, Larsson Lennart
Department of Medical Microbiology, Dermatology and Infection, University of Lund, Solvegatan 23, S-223 62 Lund, Sweden.
J Environ Monit. 2004 Apr;6(4):300-4. doi: 10.1039/b314554a. Epub 2004 Feb 26.
Muramic acid (MA) is a unique amino sugar that is a constituent of the peptidoglycan (PG) present in prokaryotic cell walls. MA can serve as a marker for quantifying bacterial load, e.g. in indoor environments, by using gas chromatography-tandem mass spectrometry (GC-MS-MS). We demonstrated recently that the methyl ester O-methyl acetate (MMA) derivative can be used to detect MA in house dust by ion-trap GC-MS-MS. However, since the MMA derivative is not formed from free MA quantification was not optimal. Here we report 1) significant improvements in sample preparation of the MMA derivative and 2) an evaluation of the performance of derivative, using for comparison the alditol acetate derivative, the gold standard in quantitative trace analysis of MA in complex matrices. The MMA derivative was analysed using an MS instrument with internal ionization and the alditol acetate derivative was analysed using an instrument with external ionization. 13C-labelled cyanobacteria, containing MA in their PG, were used as the internal standard. A linear relationship was found between the two methods in studies on 27 parallel samples of airborne dust from school classes collected on filters. Although the analytical sensitivity of the MMA derivatives was somewhat slightly lower than of the alditol acetate derivative, this may be due to differences in yield of derivative, sample clean-up efficiency, or different performance of the GC columns or MS instruments. However preparation of the MMA derivative is quick and compatible with preparation of methyl esters of 3-hydroxy fatty acids (used as markers of Gram negative endotoxin) allowing the levels of both markers to be determined in the same dust sample. In conclusion, the MMA procedure can be used to determine MA in environmental samples with good reproducibility provided the concentration of the 13C-labelled MA internal standard in the cyanobacteria is first determined with an alternative method.
胞壁酸（MA）是一种独特的氨基糖，是原核细胞壁中肽聚糖（PG）的组成成分。MA可作为量化细菌载量的标志物，例如在室内环境中，通过气相色谱 - 串联质谱法（GC-MS-MS）来实现。我们最近证明，甲酯乙酸O-甲酯（MMA）衍生物可用于通过离子阱GC-MS-MS检测室内灰尘中的MA。然而，由于MMA衍生物并非由游离MA形成，因此定量并不理想。在此我们报告：1）MMA衍生物样品制备方面的显著改进；2）对该衍生物性能的评估，使用乙酸糖醇酯衍生物作为复杂基质中MA定量痕量分析的金标准进行比较。使用具有内部电离功能的质谱仪分析MMA衍生物，使用具有外部电离功能的仪器分析乙酸糖醇酯衍生物。含有PG中MA的13C标记蓝细菌用作内标。在对过滤器上收集的27个平行的学校班级空气尘埃样本的研究中发现，两种方法之间存在线性关系。尽管MMA衍生物的分析灵敏度略低于乙酸糖醇酯衍生物，但这可能是由于衍生物产率、样品净化效率的差异，或GC柱或质谱仪的不同性能所致。然而，MMA衍生物的制备快速，并且与3-羟基脂肪酸甲酯（用作革兰氏阴性内毒素的标志物）的制备兼容，从而可以在同一样本灰尘中测定两种标志物的水平。总之，只要首先用另一种方法确定蓝细菌中13C标记的MA内标的浓度，MMA程序就可用于以良好的重现性测定环境样品中的MA。
